Crossover arrangement for multiple scanning arrays

ABSTRACT

A line scanning apparatus employing a multiplicity of linear arrays, the linear extent of which is less than the length of the scan line. To permit an entire line to be covered, the arrays are offset from one another in the direction of scan with adjoining array ends overlapped. To correct for the misalignment and redundancy introduced, the image data from the arrays is buffered until a line is completed when readout is initiated. During readout, cross over from one array to the next is effected within the overlapped areas and the redundant data discarded.

This is a continuation-in-part of application Ser. No. 793,001 filed May2, 1977.

This invention relates to raster input and output scanners and, moreparticularly to, raster input and output scanners having multiple lineararrays.

Scanning technology has progressed rapidly in recent years and todayarrays of fairly substantial linear extent are available for use inraster scanners. Indeed, the linear extent of new arrays is in somecases many times the linear extent of earlier array designs. However,the length of even these recent array designs may still not besufficient to enable a single array to span the entire width of thenormal sized line, i.e. 81/2 inches.

As a result, raster scanners often rely on shorter arrays and must,therefore, employ a multiplicity of arrays if the entire line is to bescanned in one pass. This raises the question of how to place the arraysso as to cover the entire line yet provide data representative of theline which is free of aberrations at the array junctures. Recently,interest has been expressed in optically-butted arrays. However, opticaland optical/mechanical arrangements often experience difficulty inmeeting and maintaining the tight tolerances necessary for aberrationfree scanning, particularly in operating machine environments.

It is, therefore, a principal object of the present invention to providea new and improved raster scanner employing multiple arrays.

It is an object of the present invention to provide an improved singlepass line scanner employing multiple linear arrays.

It is an object of the present invention to provide a system designed toaccommodate misalignment of plural linear arrays.

It is an object of the present invention to provide scanning apparatuswith plural relatively short linear arrays, having a composite length atleast equal to the scan width.

It is an object of the present invention to provide a line scannerincorporating plural overlapping arrays whose composite length equalsthe length of the scanned lines, with electronic means for switchingfrom one array to the next without introducing noticeable aberrationsand stigmatism.

It is an object of the present invention to provide an improved lineararray adapted to facilitate alignment between overlapping arrays.

This invention relates to a raster type input/output scanning apparatuscooperable with an input/output station to produce image datarepresentative of an image bearing original or to produce an image fromimage data, the improvement comprising at least two arrays, each of thearrays comprising a plurality of discrete operating elements arranged insuccession along the linear axis of the array, the length of each arraybeing less than the width of the area scanned, means supporting saidarrays for scanning movement relative to the station with the linearaxis of the arrays extending in a direction substantially perpendicularto the direction of scanning movement, the arrays being supported sothat the arrays overlap whereby to provide a composite array having alength at least equal to the width of the area scanned, memory means forat least temporarily storing the image data, means for actuating thearrays to scan the area, and image data transmitting means fortransmitting image data between the memory means and the arrays insuccession, the image data transmitting means crossing over from onearray to the next succeeding array within the array overlap.

Other objects and advantages will be apparent from the followingdescription and drawings in which:

FIG. 1 is an isometric view showing a raster input scanner incorporatingthe multiple array arrangement of the present invention;

FIG. 2 is a schematic illustrating an exemplary array disposition;

FIG. 3 is a schematic view of the scanner operating control;

FIG. 4 is a schematic representation of the memory buffer fortemporarily storing image data;

FIG. 5 is a schematic illustration of the data mapping arrangement toavoid bit shifting on readout from the temporary memory buffer of FIG.4;

FIG. 6 is a schematic view showing the data readout system;

FIG. 7 is a schematic illustration of the data readout with crossoverand removal of redundant data;

FIG. 8 is a schematic illustration of an alternate randomized crossovertechnique;

FIG. 9 is a schematic representation of the data readout system foreffecting randomized crossover; and

FIG. 10 is a schematic view of an imaging or output array configurationemploying paired overlapping arrays.

Referring to FIG. 1, an exemplary raster input scanning apparatus 10 isthereshown. Scanning apparatus 10, as will appear more fully hereinscans an original document 12 line by line to produce a video signalrepresentative of the original document 12. The video signal so producedmay be thereafter used to reproduce or duplicate the original 12, orstored in memory for later use, or transmitted to a remote source, etc.

Scanning apparatus 10 comprises a box-like frame or housing 14, theupper surface of which includes a transparent platen section 16 on whichthe original document 12 to be scanned is disposed face down. Adisplaceable scanning mechanism designated generally by the numeral 18,is supported on frame 14 below platen 16 for movement back and forthunderneath the platen 16 and the original document 12 thereon in the Ydirection as shown by the solid line arrow in FIG. 1.

Scanning mechanism 18 includes a carriage 20 slidably supported uponparallel rods 21, 22 through journals 23. Rods 21, 22, which parallelthe scanning direction along each side of platen 16, are suitablysupported upon the frame 14.

Reciprocatory movement is imparted to carriage 20 by means of a screwtype drive 24. Drive 24 includes a longitudinally extending threadeddriving rod 25 rotatably journalled on frame 14 below carriage 20.Driving rod 25 is drivingly interconnected with carriage 20 through acooperating internally threaded carriage segment 26. Driving rod 25 isdriven by means of a reversible motor 28.

A plurality of photosensitive linear arrays 1, 2, 3, 4 are carried onplate-like portion 35 of carriage 20. Arrays 1, 2, 3, 4 each comprise aseries of individual photosensitive picture elements or pixels 40arranged in succession along the array longitudinal axis. The arraysscan the original document 12 on platen 14 as scanning mechanism 18moves therepast, scanning movement being in a direction (Y)substantially perpendicular to the array longitudinal axis (X). As bestseen in FIG. 2, the arrays 1, 2, 3, 4 may, due to the difficulty inaccurately aligning the arrays one with the other, be offset from oneanother in the direction of scanning movement (the Y direction). Toaccommodate the relatively short length of the individual arrays, thearrays overlap. In the exemplary illustration, the end portion of arrays2, 1, 4 overlap the leading portion of the succeeding arrays 1, 4, 3when looking from left to right in FIG. 2 along the X direction.

As will be understood, the length of the individual arrays 1, 2, 3, 4may vary with different types of arrays and from manufacturer tomanufacturer. As a result, the number of arrays required to cover theentire width of the original document 12 may vary from that illustratedherein.

Photosensitive elements or pixels 40 of arrays 1, 2, 3, 4 are normallysilicon with carrier detection by means of phototransistors,photodiode-MOS amplifiers, or CCD detection circuits. One suitable arrayis the fairchild CCD 121-1728 pixel 2-phase linear array manufactured byFairchild Corporation. As described, arrays 1, 2, 3, 4 are offset fromone another in the scanning or sagittal direction (Y direction) but withan end portion of each array overlapping the leading portion of the nextsucceeding array to form in effect a composite unbroken array.

To focus the image onto the arrays 1, 2, 3, 4 a lens 43 is provided foreach array. Lenses 43 are supported on carriage 20 in operativedisposition with the array 1, 2, 3, 4 associated therewith. Mirrors 44,45 on carriage 20 transmit the light images of the original via lenses43 to arrays 1, 2, 3, 4. Lamp 48 is provided for illuminating theoriginal document 12, lamp 48 being suitably supported on carriage 20.Reflector 49 focuses the light emitted by lamp 48 onto the surface ofplaten 16 and the original document 12 resting thereon.

In operation, an original document 12 to be scanned is disposed onplaten 16. The scanning mechanism 18 including motor 28 is actuated,motor 28 when energized operating driving mechanism 24 to move carriage20 back and forth below platen 16. Lamp 48 is energized during thescanning cycle to illuminate the original document 12.

To correlate movement of carriage 20 with operation of arrays 1, 2, 3, 4an encoder 60 is provided. Encoder 60 generates timing pulsesproportional to the velocity of scanning mechanism 18 in the Ydirection. Encoder 60 includes a timing bar 61 having a succession ofspaced apertures 62 therethrough disposed along one side of the path ofmovement of carriage 20 in parallel with the direction of movement ofcarriage 20. A suitable signal generator in the form of a photocell-lampcombination 64, 65 is provided on carriage 20 of scanning mechanism 18with timing bar 61 disposed therebetween.

As carriage 20 of scanning mechanism 18 traverses back and forth to scanplaten 16 and any document 12 thereon, photocell-lamp pair 64, 65 ofencoder 60 moves therewith. Movement of the photocell-lamp pair of 64,65 past timing bar 61 generates a pulse-like output signal in outputlead 66 of photocell 64 directly proportional to the velocity ofscanning mechanism 18.

As can be envisioned by those skilled in the art, supporting arrays 1,2, 3, 4 in exact linear or tangential alignment (along the X-axis) andmaintaining such alignment throughout the operating life of the scanningapparatus is extremely difficult and somewhat impracticable. To obviatethis difficulty, arrays 1, 2, 3, 4 are initially mounted on carriage 20in substantial tangential alignment. As can be seen in the exemplaryshowing of FIG. 2, this nevertheless often results in tangential arraymisalignment along the x-axis. If the disposition of the arrays 1, 2, 3,4 is compared to a predetermined reference, such as the start of scanline 101 in FIG. 2, it can be seen that each array 1, 2, 3, 4 isdisplaced or offset from line 101 by some offset distance d₁, d₂, d₃,d₄, respectively. As will appear more fully herein, the individualoffset distances of each array 1, 2, 3, 4 is determined and the resultprogrammed in an offset counter 120 (FIG. 3) associated with each array.Offset counters 120 serve, at the start of the scanning cycle, to delayactivation of the array associated therewith until the interval d₁, d₂,d₃, d₄, therefor is taken up.

Referring to FIG. 3, the pulse-like signal output of encoder 60 which isgenerated in response to movement of carriage 20 in the scanningdirection (Y-direction), is inputted to a phase locked frequencymultiplier network 100. Network 100, which is conventional, serves tomultiply the relatively low frequency pulse-like signal input of encoder60 to a high frequency clock signal in output lead 103. Feedback loop104 of network 100 serves to phase lock the frequency of the signal inlead 103 with the frequency of the signal input from encoder 60.

As will be understood, changes in the rate of scan of carriage 20produce a corresponding change in the frequency of the pulse-like signalgenerated by encoder 60. The frequency of the clock signal produced bynetwork 100 undergoes a corresponding change. This results in a highfrequency clock signal in output lead 103 directly related to thescanning velocity of carriage 20.

The clock signal in output lead 103 is inputted to programmablemultiplexer 106. The output of a second or alternate clock signal sourcesuch as crystal controlled clock 108 is inputted via lead 109 tomultiplexer 106. Multiplexer 106 selects either network 100 or clock 108as the clock signal source in response to control instructions (CLOCKSELECT) from a suitable programmer (not shown). The selected clocksignal appears in output lead 111 of multiplexer 106.

An operating circuit 114 is provided for each array 1, 2, 3, 4. Sincethe circuits 114 are the same for each array, the circuit 114 for array1 only is described in detail. It is understood that the number ofcircuits 114 is equal to the number of arrays used.

Operating circuit 114 includes a line transfer counter 115 forcontrolling the array imaging line shutter time for each scan. Counter115 is driven by the clock signal in output lead 111 of multiplexer 106.It is understood that where the signal input to counter 115 comprisesthe clock signal produced by network 100, array sample size remainsconstant irrespective of variations in the velocity of carriage 20. Inother words, where carriage 20 slows down, array shutter time becomeslonger. If carriage 20 speeds up, array shutter time becomes shorter.

Initial actuation of line transfer counter 115 is controlled by theoffset counter 120 associated therewith. Offset counter 120, which isdriven by the clock signal in output lead 111, is preset to toll a countrepresenting the time interval required for array 1 to reach start ofscan line 101 following start up of carriage 20. On tolling the presetcount, offset counter 120 generates a signal in lead 122 enabling linetransfer counter 115.

It will be understood that the offset counters 115 associated with thecircuits 114 for the remaining arrays 2, 3, 4 are similarly preset to acount representing the distance d₂, d₃, d₄, respectively by which arrays2, 3, 4 are offset from start of scan line 101.

Referring particularly to FIG. 2 each array 1, 2, 3, 4 scans a portionof each line of the original document 12, the sum total of the data(less overlap as will appear more fully herein) produced by arrays 1, 2,3, 4 representing the entire line. Preferably, arrays 1, 2, 3, 4 are ofthe same size with the same number of pixels 40. As described, the linetransfer counters 115 of circuits 114 control the array imaging lineshutter time for each scan, counters 115 being preset to activate thearray associated therewith for a preselected period for this purpose.Scanned data from the arrays 1, 2, 3, 4 is clocked out by clock signalsderived from a suitable pixel clock 118.

Sampled analog video data from the arrays 1, 2, 3, 4 is fed to asuitable video processor 148 which converts the video signals to abinary code representative of pixel image intensity. The binary pixeldata from processor 148 is mapped into segments or words by Pixel DataBit Mapper 149 for storage in offset relation in RAM 175 as will appear.Bit Mapper 149 is driven by clock signals from pixel clock 118. Datafrom Bit Mapper 149 is passed via data bus 174 to RAM 175 where the datais temporarily stored pending receipt of data from the array which lastviews the line. In the exemplary arrangement illustrated, the last arraywould be array 4.

Multiplexer 150 may be provided in data bus 174 to permit data fromother sources (OTHER DATA) to be inputted to RAM 175.

The binary data is stored in sequential addresses in RAM 175 (see FIG.4), the data being addressed into RAM 175 on a line by line basis by theRAM address pointers 165 through Address Bus 180. The clock signaloutput from pixel clock 118 is used to drive address pointers 165. Linescan counter 170, which is driven by the output from line transfercounter 115, controls the number of full scan lines that will be storedin RAM 175 before recycling. The output of counter 170 is fed to RAMAddress pointer 165 via lead 119. It is understood that line scancounters 170 are individually preset to reflect the degree of arrayoffset in the Y-direction.

Ram 175 provides a buffer for scanned data from each array, RAM 175buffering the data until a full line is completed following which thedata is read out. A suitable priority encoding system (not shown) may beused to multiplex the data input from arrays 1, 2, 3, 4 with the addressassociated therewith. Ram 175 has input and output ports for input andoutput of data thereto.

Since the degree of misalignment of arrays 1, 2, 3, 4 in the Y-directionmay vary, the storage capacity of RAM 175 must be sufficient toaccommodate the maximum misalignment anticipated. A worse casemisalignment is illustrated in FIG. 4 wherein it is presumed that arrays1, 2, 3, 4 are each misaligned by a full line. In that circumstance andpresuming scanning of line l is completed, RAM 175 then stores the linedata for lines l, l₁, l₂, l₃, l₄ from array 1, lines l, l₁, l₂, l₃ fromarray 2, lines l, l₁ , l₂ from array 3, and lines l, l₁ from array 4.The blocks of binary data that comprise the completed line 1 are incondition to be read out of RAM 175. In the above example, an extra lineof data storage is provided.

Line scan counters 170 are recycling counters which are individuallypreset for the number of lines of data to be stored for the arrayassociated therewith. As a result, address pointers 165 operate in roundrobin fashion on a line by line basis. On reaching a preset count, thesignal from counters 170 recycle the address pointer 165 associatedtherewith back to the first storage line to repeat the process. It isunderstood that prior thereto, that portion of RAM 175 has been clearedof data.

As described, data from video processing hardware 148 is storedtemporarily in RAM 175 pending completion of the line. In placing thedata in RAM 175, the data is preferably mapped in such a way as to avoidthe need for subsequent data bit shifting when outputting the data.Referring to FIG. 5, wherein mapping of pixel data from arrays 1, 2 isillustrated, data from an earlier array (i.e. array 1) is mapped byPixel Data Bit Mapper 149 (FIG. 3) into segments or words 180 beforebeing stored in RAM 175. The first pixel (P₁ -1) of the array within thearray overlap 181 is mapped into a known bit position within the segmentor word 180 at the point of overlap.

At the end of line transfer, the first pixel (P₁ -2`) of the succeedingarray (i.e. array 2) is clocked into the bit position (P₁ -1) of thefirst overlapped pixel of the previous array. This correlates the firstoverlapping pixel (P₁ -2) of the succedding array (i.e. array 2) withthe first overlapped pixel (P₁ -1) of the preceding array (i.e. array1). Crossover from one array to the succeeding array on data readout maythen be effected without the need to shift bits.

Referring now to FIGS. 6 and 7, video data held in RAM 175 is read outto a user (not shown) via RAM output bus 176, in both tangentially andspatially corrected form, line by line, through output channel 200. Datareadout is controlled by a microprocessor, herein CPU 204 in accordancewith address program instructions in memory 206. CPU 204 may compriseany suitable commercially available processor such as a Model M6800manufactured by Motorola, Inc.

The address program instructions in memory 206 include a descriptor list207. List 207 contains information identifying the number of bits to beread out (N_(n)), the address of the first word (A), and other userinformation (U). The DATA OUT address information is fed to addressmultiplexer 208 via address bus 209.

As described heretofore, exact tangential alignment and end to endabutment of multiple arrays is difficult to achieve. In the arrangementshown, sagittal misalignment (in the Y direction) among the arrays isaccommodated by offset counters 120 of the individual array operatingcircuits 114. The need to accurately abut the arrays end to end isobviated by overlapping succeeding arrays.

As a result of the above, the sequence in which video data is inputtedto RAM 175 offsets sagittal misalignments between the several arrays. Byoutputting the data from RAM 175 on a line by line basis, the lines arereconstructed without sagittal misalignment.

Due to the overlapping disposition of arrays 1, 2, 3, 4, data within theoverlapping portions of the arrays is redundant. To obviate this andprovide a complete line of data without repeated or redundant portions,bit crossover on readout within the overlapping regions is used.

Referring now to the embodiment shown in FIG. 7, data bit crossoverwithin the overlapping portions of arrays 1, 2, 3, 4 is effected by analgorithm which picks a predetermined last cell to be sampled within theoverlapped region and automatically picks the next bit in the succeedingarray. In the descriptor list 207 illustrated in FIG. 7, the total bitoutput from the first array is N₁ bytes+n₁ bits with the bit output fromthe second array N₂ bytes-n₂ bits. In the example shown in FIG. 7,crossover from array 2 to array 1 is effected between bit 4 and bit 5.

In the embodiment shown in FIGS. 8 and 9, bit crossover from one arrayto the other during readout of data from RAM 175 is effected, within thearray overlapping region, on a randomized basis. As described, the imagedata is mapped into sequences or words 180 by Bit Mapper 149. Randomizedcrossover is effected by varying either or both of the byte (N) and bit(n) selections within the crossover area.

In the embodiment shown, a suitable random number generator 218, whichis driven by the clock output of pixel clock 118, generates randomizedcount sequences within the crossover limits from each array pair. Memory206 uses the count output of generator 218 to vary the byte/bit addressof descriptor list 207 (FIG. 7). As a result, the point at whichcrossover from one array to the next succeeding array takes place varieswith each line.

In the example shown in FIG. 8, array crossover is effected on readoutof the first line (l₁) between bits N₁ +n₁ and N_(2`-n) ₂ ; for thesecond line (l₂) between bits N₁ +(n₁ +1) and N₂ -(n₂ +1), and betweenbits (N₁ +1)+n₁ and (N₂ -1)-n₂ of the third line.

While the invention herein has been described in exemplary fashion in araster type input or scanning apparatus environment, it will beunderstood that the principles of the present invention may be utilizedwith raster type output, i.e. imaging, devices. In that type ofapplication, multiple imaging elements, herein, imaging arrays 500, arearranged in succession upon a support structure or base as in the caseof the photosensitive linear arrays 1, 2, 3, 4 described heretofore. Theimaging arrays 500 are disposed with the adjoining ends thereofoverlapping to enable the entire length of the line to be covered byarrays whose individual linear extent is less than the line length.

Referring to FIG. 10, an exemplary arrangement is shown employing pluralimaging arrays 500, 500' disposed so that the adjoining ends 501, 501'overlap. Imaging arrays 500, 500' are each comprised of a plurality oflight emitting diodes (L.E.D.s herein) 505 mounted in succession upon asuitable base 506. Arrays 500, 500' are arranged in operative exposurerelationship with the relatively movable photoconductive member 508 of axerographic apparatus (not shown).

As understood by those skilled in the xerographic arts, exposure of thephotoconductive member 508, which has been previously uniformly chargedby a suitable corona type charging device, discharges the chargedportions of member 508 in a pattern corresponding to the illuminationpattern of L.E.Ds 505. The latent electrostatic image created thereby onphotoconductive member 508 is thereafter developed with suitableelectroscopic marking material, i.e. toner. The developed image may bethen transferred to a suitable copy substrate material, i.e. paper, andfused to provide a permanent copy of the image.

Imaging arrays 500, 500' may be loaded with binary image data from asuitable source such as random access memory (RAM) 515 throughserial-to-parallel buffers 516, 516'. The output gates of buffers 516,516' are coupled to the individual L.E.D.s 505 comprising exposurearrays 500, 500' through control gates 518, 518'. A suitable triggersource (not shown) enables gates 518, 518' following loading of the lastbit of image data in the buffer 516, 516' associated therewith.

In operation, the output gates of buffers 516, 516' are loaded with abinary signal pattern representative of the image data stream inputedthereto. On enabling of gates 518, 518', individual L.E.D.s are actuatedin accordance with the binary signal pattern to dischargephotoconductive member 508 in correspondence with the image data.

To prevent repetitive exposure of photoconductive member 508 in areaswhere exposure arrays 500, 500' overlap, crossover is madeelectronically from array 500 to array 500' within the overlapping areas501, 501'. Crossover may be effected by a controlling algorithm whichpicks on either a fixed or random basis a predetermined image bit withinthe overlapping area as the last image bit for imaging array 500 and thenext image bit of the data stream as the first image bit for imagingarray 500'. In this circumstance, the image data flows from memory 515to output buffers 505,505' and arrays 500, 500' rather than from thearrays (i.e. arrays 1, 2, 3 and 4) to output bus 176 as describedheretofore. Buffers 516, 516' are loaded with data bits corresponding tothe L.E.D.s 505 to be used in each array 500, 500'.

For example, if it be assumed that each image line comprises 2000 imagebits and that each imaging array 500, 500' has 1100 L.E.D.s, the arrayoverlap totals 200 L.E.D.s and falls in the range of 1000 and 1200 imagebits. If the crossover point is selected between image bits 1099 and1100, buffer 516 would be loaded with image bits 0-1099 and buffer 516'loaded with image bits 1100-2000. The L.E.D.s of array 500 correspondingto image bits 1100-1200 would not be used. Similarly, the L.E.D.s ofarray 500' corresponding to image bits 1000-1099 would be unused in thiscrossover example. If the crossover point is fixed, crossover from array500 to array 500' would repeatedly occur between image bits 1099 and1100 in the example provided. If the crossover point is selected onrandom basis, crossover from array 500 to array 500' might take placefor example between bits 1090 and 1091 for the next line, between bits1120 and 1121 for the line after that, and so forth and so on.

While an overlapping exposure array pair 500, 500' has been illustratedand described herein, it will be understood that the principles of theinvention are applicable to exposure array configurations employing morethan two arrays.

Further, imaging array constructions employing multiple imaging devicesother than L.E.D.s 505 and which may produce for example, copy paper,may be contemplated as, for example, exposure arrays comprised ofmultiple injection lasers or laser diodes, or printing arrays comprisedof multiple ink jets, or electrostatic writing arrays comprised ofmultiple electrostatographic styli, or thermo magnetic (i.e. Curiepoint) arrays comprised of multiple thermal heads, or ferro magneticimaging arrays comprised of multiple magnetic recording heads.

While the invention has been described with reference to the structuredisclosed, it is not confined to the details set forth, but is intendedto cover such modifications or changes as may come within the scope ofthe following claims:

What is claimed is:
 1. In a raster imaging apparatus for producingimages on a member in response to image signals, the improvementcomprising:at least two imaging arrays, each of said arrays comprising aplurality of discrete imaging elements arranged in succession along theimaging axis of said array, the length of the area imaged by each ofsaid arrays being less than the width of said member along said imagingaxis; means supporting said arrays for movement relative to said memberwith the imaging axis of said arrays extending in a directionsubstantially perpendicular to the direction of said movement; saidarrays being supported so that the areas imaged by each of said arraysoverlap whereby to provide a composite imaged area; and image signalinput means for inputting image signals to said array imaging elementsto actuate said imaging elements selectively in accordance with saidimage signals to produce images on said member, said image signal inputmeans including crossover means for crossing over from one array to thenext succeeding array within the overlapping portion of the areas imagedby each of said arrays on a random basis.
 2. The raster imagingapparatus according to claim 1 in which said crossover means changes thecrossover point between said arrays following a predetermined block ofimage signals.